Infrared Absorption Spectra of Urea-formaldehyde Initial Condensation Products. II. Dimethylurea

Abstract

Abstract The infrared absorption spectra of symmetric and asymmetric dimethylurea have been observed in the 4000—400 cm−1 region. In order to investigate the amide characteristic bands, the spectra of CH3NHCONHCH3 and CH3NDCONDCH3 have also been measured in the solid and liquid states, and in solutions. The in-plane normal vibrations of these molecules have been calculated. As a result of our measurements and calculations, it has been found that: (1) The contribution of the polar resonance structure of asymmetric dimethylurea is small compared with that of symmetric dimethylurea, and molecular geometry contributes to the formation of hydrogen bonding. (2) From the position of the amide bands, the molecular configuration of symmetric dimethylurea is the “trans” form as well as that of methylurea. (3) The results of normal coordinate analysis show a good agreement with that observed within an average deviation of 2.6%.